Q. Can Table 310.15(B)(6) be used to size service conductors for a duplex?

A. Maybe. Table 310.15(B)(6) is only suitable to size 3-wire, single-phase, 120/240V service or feeder conductors (including neutral conductors) that serve as the main power feeder for an individual dwelling unit. So you can size the individual service conductors to each unit using this table, but not the service conductors for both units.